1. Field of the Invention
The present invention relates to method for direct bonding a member having nitride surface to another member having a nitride or oxide surface. For the first member, a non-nitride member having its surface covered with nitride or a member entirely made of nitride can be used. As the other member, a member having its surface covered with nitride or oxide, a member entirely made of nitride or oxide, metal, a semiconductor material, ceramic, a polymeric compound or the like can be used. The direct bonding method is used to form a bond between a base and IC chips or sensors which have surfaces covered with a protective film such as Si.sub.3 N.sub.4 or TiN. Further, the direct bonding method is used for precisely bonding base to another member such as a super-hard member, a super-heat resisting member or the like.
2. Description of Related Art
A conventional method for direct bonding of two materials is disclosed in Japanese Unexamined Patent Publication No. hei 6-302486. In the conventional direct bonding method, hydroxide groups are chemically adsorbed on the surface of a member in a vacuum atmosphere, then two members are pressed together tightly so that two materials are directly bonded through the use of hydrogen bonds between the surfaces of the two members.
However, in the above-described method, it is necessary to adsorb hydroxide groups to the surface of one bonding member, that is, it is a necessary condition that the surface can be oxidized. Because nitride does not adsorb hydroxide groups, a nitride member or a member covering the surface with nitride is not used as a member for adsorbing hydroxide groups. Thus, it is impossible to form a bond between two members having a nitride body or nitride cover film on the surface, or between such a nitride member and another member such as a metal and semiconductor member without adsorbing hydroxide groups.
As a conventional method of bonding nitride and metal, metal atoms are driven into the surface of a nitride member at a high energy so that the surface of nitride is metallized. Then, the nitride and metal are compressed at a high pressure of above 100 MPa to tightly contact one another, or an insert member which conforms to both bonding members is sandwiched between the nitride member and the metal member, and the two bonding materials are pressed together at a high temperature.
As described above, the conventional method does not directly bond between the nitride members or between the nitride member and a non-metal member. Further, in the bonding method of nitride and metal, the metal for bonding must have good ductility, the method requires a high temperature of direct lower melting point and a high pressure of above 100 MPa.
Thus, in the above-described bonding methods, the size and the shape of bonding member and bonding precision have limits. Particularly, when metal and a member which is made with nitride material having a complex shape at the microscopic level are bonded, deformations and cracks are generated in this member after bonding so that the method cannot be used for precise bonding.